There are proposed various heat spreaders for spreading heat generated from an IC chip mounted on an IC package.
For example, JP-2563182-B describes a heat sink attaching apparatus in which a gate array is mounted inside a space (cavity) defined by a frame, and a finned heat sink is provided to make contact with a top surface pad of the gate array, thereby spreading heat generated from the gate array.
While the heat spreading efficiency of the above-mentioned heat sink is good as it is provided with plural fins laminated along a post, such structure is complicated, and the operation (catching the post with a hole formed in a heat sink clip by inserting the heat sink clip between two of the fins) required for attaching the heat sink is cumbersome.
Thus, there is a demand for a heat spreader which has a simple structure, and can be easily attached. For example, a so-called hat type heat spreader as shown in FIGS. 10A and 10B is proposed.
As illustrated in FIGS. 10A and 10B, a heat spreader 100 has a top wall 101, a circumferential wall 102 formed continuously from the entire circumference of the top wall 101, and a flange 103 extended outwardly from the bottom edge of the circumferential wall 102.
For example, it is assumed that an IC chip is mounted on a circuit board as an IC package, and the circuit board is mounted on a motherboard together with a socket. The above-mentioned heat spreader 100 is mounted on the circuit board to surround the IC chip, and then, the heat spreader 100 is attached to the socket together with the circuit board. At that time, the flange 103 of the heat spreader 100 is pressed by a turnable lid member of the socket. Consequently, plural connection terminals formed on the bottom surface of the circuit board are electrically connected to plural connection bumps formed on a base substrate of the socket, respectively.
Here, while the flange 130 is formed on the entire circumference of the circumferential wall of the heat spreader 100, only a part of the whole area of the flange 130 is to be pressed by the lid member of the socket, and the remained non-pressed part is a waste.
On the other hand, in an IC package, the number of chips mounted on a circuit board has been recently increased due to the advance of the implementation of a multichip structure, and the size of the circuit board is correspondingly increased.
Sometimes, the multichip structure is restrained, depending upon the shape of a heat spreader. Thus, it is requested to increase the cavity volume of the heat spreader so that it can cover each IC chip in the IC package, in order to assure the flexibility of the implementation of the multichip structure.